Live virus vectors represent a powerful tool for vaccine delivery. This application seeks funding to test the feasibility of using the paramyxovirus simian virus 5 (SV5) to deliver different antigen doses to elicit neutralizing antibody and antiviral CTL responses to HIV antigens. SV5 is a common and non-pathogenic nonsegmented negative sense RNA virus with inherent properties that could be exploited to develop a new class of vaccine vectors. In the first aim, recombinant SV5 vectors will be engineered to encode the HIV gp160 envelope protein in either a 3'-proximal or 3'-distal position in the genome, and it is anticipated that this will result in high and low transcription of the gene, respectively. Biochemical approaches will be used to determine the growth characteristics of the rSV5 vectors and the gp160 expression levels in tissue culture cells. The results will identify candidate SV5 vectors that have a balance between optimum growth to high titers and differential synthesis of the HIV glycoprotein. In the second aim, mice will be vaccinated with the rSV5-gp160 vectors and the serum will be tested for their ability to neutralizing HIV infectivity in tissue culture. These experiments will test the hypothesis that higher levels of HIV antigen expression result in higher titers of neutralizing antibody. The investigator's published work has shown that high avidity CD8+ cytotoxic T lymphocytes (CTL) can be preferentially expanded in vitro by stimulation with low concentrations of peptide antigen, and that the high but not low avidity CTL efficiently cleared a viral infection in vivo. We intend to exploit the polarity of SV5 transcription to generate vaccine vectors expressing differential levels of HIV antigen, with the intent of mimicking in vivo what we have done previously in vitro by varying the peptide concentration. In the third aim, we will test the hypothesis that high avidity CTL can be preferentially elicited with SV5 vectors expressing low levels of HIV antigen. CTL will be isolated from mice previously infected with rSV5-gp160 vectors that express differential levels of the HIV glycoprotein. The anti-gp160 CTL activity and precursor frequency of high and low avidity CTL will be determined. At the completion of this work, it is anticipated that a vector system which may be designed to yield novel multivalent HIV vaccines capable of simultaneously delivering high antigen levels (3'-proximal) for antibody responses and the low level antigen expression (3'-distal) required for eliciting high avidity CTL will be developed.